Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...

I asked Oliver about using one of these to stack a Quark
( Beloptik H-alpha bandpass filter FWHM 1.5A 0.15nm )
and about image brightness for visual use....and received the following
response back today

Dear Brian,

Yes I can do it. My personally experience with some Quark's (4pcs) are not so good. The quality of the Quark is too different in bandpass/FWHM and brightness. I do not recommend it.

Clear skies
Oliver

So very honest of him ... are there any other cheap methods of stacking
a quark for visual use at all ?

I got the same Valery, my images were vignetted. But, visually the results were very impressive offering a lot more contrast on the native quark. I just haven't had the clear skies to experiment with this as much as I would like this summer.

marktownley wrote:I got the same Valery, my images were vignetted. But, visually the results were very impressive offering a lot more contrast on the native quark. I just haven't had the clear skies to experiment with this as much as I would like this summer.

Yes, Mark. Visually the effect is great. This is because a human eye has MUCH MUCH higher dynamic range in the brightness sensitivity. And it just compensite the brightness difference due to vignetting. Not so with a CCD detector or CMOS. We need to supress all the brightness range in to only 8 bit and then present it on a B/W monitor where we surely can see only 32 brightness gradations or 5 bit only! So, even slightest vignetting will be easily seenin such data presentation and only total or almost total absence of vignetting will be seen on the screen as no vignetting factor here.
The vignetting in this pair of etalons is huge if to see it on a screen.

So, this mostly a visual mod, not good enough for imaging.

Valery.

Last edited by Valery on Mon Aug 10, 2015 5:36 pm, edited 1 time in total.

"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Merlin66 wrote:Why would you want to double stack a Quark which is already around 0.3A bandwidth??? (Because we can!??)

You're right, because we can; and even if someone says we can't we still try anyway

Seriously though, a ss etalon, even one with a low bandpass 0.3a for example, still has continuum leakage in the wings - this is why we see the spicule ring around the edge of the sun. As soon as an etalon is double stacked the shape of the transmission changes, not just a narrower pass, but also how much less is transmitted off band - see the pic:

Coro-60mm-profile.JPG (184.36 KiB) Viewed 3018 times

As a result the signal to noise ratio is higher and we get a higher contrast.

I'm sure Valery with enough sunshine time it could be developed to make it better for imaging, but, like i've mentioned before sun time has been at a real premium this year with barely enough time for normal imaging, let alone mod testing...

You can reduce the filter bandpass/FWHM of your Quark with a Coronado PST etalon without both collimating lenses. Replace the second 200mm positive pcx lens with a dia. 1inch #29 or Schott RG630 dark red filter for reduce reflexions from eyepiece side. You need an adapter M35/M50 and M50/1.25" barrel.

Finesse -- or transmission profile -- means everything, and the "tail suppression" shown for the Coronado 0.7 vs. 0.5 DS (e.g. better finesse) is even more relevant when you consider the 0.5 curve is "normalized" to give the same peak transmission.

In reality, the peak transmission -- and more importantly transmission tails -- are about half the amplitude shown:

Stack transmission to scale.jpg (71.91 KiB) Viewed 2945 times

This leads to an even more dramatic suppression of continuum than one would assume from the normalized curves themselves.

Stacking etalons dramatically improves the finesse of a given etalon system, therefore filter system design (single verses multiple cavities) is more important than bandpass...

I conclude (and DayStar has stated) that their filters are single cavity filters -- therefore they don't appear to have the transmission profile (finesse) that results from a double stacked etalon system, even though they may have equal or narrower FWHM specs.

Bob,
I re-read your CN posting but still have problems with your 'double edge' = continuum leakage.
The spicule edge region is visible on band and off band....at 0.3 FWHM even with the "tails" you are still working within the wings of the Ha....
OK
My real issue is when you use a spectroheliograph (SHG) to generate a solar spectrum and then extract a strip from the absorption line the bandwidth of which will depend on the dispersion of the spectrograph and the PSF of the instrument. I'd like to think, that at least in theory, the extraction say of a 0.3A wide strip (based on a dispersion of >0.05 A/pixel and a measured resolution (using a neon reference line) of <0.1A) would NOT give the same "leakage" results of the etalons etc. but an almost "clean" 0.3A image with NO side band interference.
I have had images submitted for the new book on the digital SHG which don't show a double limb (but plenty of spicules!!).
Any comment?

First, I have ZERO experience with SHG’s, so I can’t comment with an absolute conclusion on how they perform or what they actually show at the narrow bandpass you describe -- but I have a postulate based on both my own observation as well as reading and journal research. The vast majority of my experience is with a 0.7 FWHM ATM DayStar filter I purchased in 1976, followed by a ~ 0.5 FWHM Coronado SM90/90 DS system I purchased in 2003.

Over the years I have seen various references to features that often seemed to confuse or misidentify features near the limb, most significantly, the so-called “spicule fringe,” which in reality is the entire chromosphere - including spicules - highlighted by the edge of the photosphere which is visible in wider bandpass filters on-band due to continuum leakage from the filter transmission tails:

"Spicules" that are visible in the above image are a combination of macro spicules visible above what Harold Zirin (Astrophysics of the Sun) calls the “general chromosphere” – which includes prominences, etc. – and the true spicule layer which lies slightly below the general chromosphere and is more off-band due to Doppler shifting:

Above we can see the filter being tuned from the one side of the H alpha line to the other (note how the photosphere becomes brighter as we move off-band). The true spicule layer - being largely Doppler-shifted to either side of the line - is much more prominent off-band, and much less visible when on-band, where the general chromosphere becomes visible and dominates the spicules which lie off-band. The photosphere is also continuously visible due to the leakage of continuum from the filter system tails. I believe this is how the misnomer of “spicule layer” for the general chromosphere originated from the lay solar observing community.

I re-read your CN posting but still have problems with your 'double edge' = continuum leakage.
The spicule edge region is visible on band and off band....at 0.3 FWHM even with the "tails" you are still working within the wings of the Ha....

With a narrower band-pass and higher finesse filter system, it becomes more obvious where the true spicule layer lies, and the edge of the photosphere is eliminated when tuned on-band:

(a) An off-band chromospheric image. Several arrows mark the locations of dark and bright spicules crossing the limb. The spicule is brighter than the sky, but normally is in absorption against the disk, even near the extreme limb. (b) A centerline image at the same position angle but a few hours later showing the inner limb due to sidebands of the Zeiss (Lyot) filter. (c) A limb image on a different date with a pure filter (Rakuljic filter), with the inner limb barely detectable from the morphology.

The image through this pure filter [the Rakuljic (Rakuljic & Leyva 1993 ) holographic filter] does not show the spurious inner limb, which was shown by White and Simon (1966) to be due to continuum passing through the Lyot filter sidebands...

... Images in the wing of H-alpha show Doppler-shifted moving features in the chromosphere, namely spicules. Despite the evidence of the Dunn-Zirker images and various eclipse measurements, there is a general belief among solar physicists that the general chromosphere extends only to 2000 Km, as in the VAL model (Vernazza, Avrett & Loeser 1981). It is thought that the higher H-alpha emission is due to spicules. Our result establishes the qualitatively obvious fact that, except for macrospicules, the general chromosphere extends above the average spicules.

The off-band (spicule) limb is always lower than the centerline limb by an average value of 500 Km (0.7 arcsec). Because of the self reversal of the chromospheric H-alpha line, the off-band chromosphere is twice as bright as the centerline. As a result, the gradient of the off-band limb profile is considerably steeper just above the photosphere. Thus the popular view that spicules rise above the chromosphere is incorrect, except insofar as the macrospicules are concerned.

Thus it can be seen the effect of continuum leakage -- “the side bands of the Zeis (Lyot) filter” -- produces the perception of a “spicule layer,” via showing the “inner limb” -- the photosphere.

My own experiment using my double stacked < 0.5 Å system shows an on-band image with the general chromosphere – including prominences and macro-spicules (top) with no photospheric leakage (no "double limb'), while when tuned to the blue wing the general chromopshere disappears, and the spicule layer becomes evident, with the limb of the photosphere becoming visible as we venture father off-band and out of the center of the absorption line (bottom):

on v off band 0.5 A.jpg (62.55 KiB) Viewed 2895 times

I have had images submitted for the new book on the digital SHG which don't show a double limb (but plenty of spicules!!).

I therefore believe this is a technical or semantic differentiation of terms between spicules themselves and macro spicules, which are a different beast altogether. Even at a very narrow 0.3 Å FWHM on-band with a SHG, I would expect to see macro-spicules, along with the general chromosphere, and no double-limb or ‘double-edge’ from the leakage of continuum.I would not expect to see the ‘real’ spicule layer, which should from the above discussion be less visible with a narrower FWHM and be buried below and within the general chromosphere when on-band.